Atlas is the first cervical bone. It’s an atypical cervical vertebra.It has no body, no spinous process, it is ring like consists of anterior and posterior arches and two lateral masses. The anterior and posterior arches provide attachment for a broad, dense fibrous anterior atlanto-occipital membrane and a broad but relatively thin posterior atlanto-occipital membrane. The posterior arch of atlas has a groove for passing of 3rd part of vertebral artery.
In the present study 80 dry atlas bones were studied out of which in 2 atlas vertebrae the lateral tendinuous part of the posterior atlanto-occipital membrane had been ossified and converted the groove into a foramen. This is one of the sites where the vertebral artery can get compressed leading to ischaemia in the regions supplied by it. Also in old age due to the reduced elasticity of the arteries can play a role in symptom of giddiness and syncope?The knowledge of such type of variation is important for anatomists, neurosurgeons, orthopedicians and interventional radiologists who operate in this region. Significance of study in the clinical practice has been discussed here.